In service station environments, fuel is delivered to fuel dispensers from underground storage tanks (UST), sometimes referred to as fuel storage tanks. USTs are large containers located beneath the ground that hold fuel. A separate UST is provided for each fuel type, such as low octane gasoline, high-octane gasoline, and diesel fuel. In order to deliver the fuel from the USTs to the fuel dispensers, typically, a submersible turbine pump (STP) is provided that pumps the fuel out of the UST and delivers the fuel through a main fuel piping conduit that runs beneath the ground in the service station. Other types of pumps other than a STP, such as a self-contained pump within the dispenser housing for example, may be employed.
A shear valve employs a single-stage main poppet valve that controls the flow of fuel through the shear valve. The main poppet valve is located inside the shear valve in the fuel flow path. When the shear valve is opened, fuel is allowed to flow. When the shear valve is closed, in response to a shear or other safety condition, fuel flow is prevented. After the safety condition is remedied, it is necessary to reset the shear valve to open the main poppet valve to allow fuel flow. The main poppet valve is manually reopened.
However, a large amount of force may be necessary to open the main poppet valve, making it very difficult or impossible to open and reset the shear valve. For example, if there is pump pressure trapped on the upstream side of the main poppet valve and little or no pressure or atmospheric pressure on the downstream side, more force than can be provided may be required to open the main poppet valve to reset the shear valve after the main poppet valve is closed. Thus, opening the main poppet valve may be difficult for service personnel. Application of force to open the main poppet valve may damage the shear valve and make it unusable. Damage to the shear valve may go unnoticed by service personnel.
Thus, the present invention provides a shear valve that requires less force to open the main poppet valve in case there is a substantial pressure differential across the valve after it is closed.